Among laboratory-bred Biomphalaria glabrata, a live snail in an anomalous shell was found. The anomaly consisted in changes of level in the whorls. The specimen was isolated for a study on its biological behaviour. Afterwards, another specimen displaying a similar anomaly was joined to it. The results obtained showed their biological functions to be normal, their anomaly being of genetic character. In F1 embryos, the anomaly observed was 0.01%. In a 25-month period of investigation, 13 anomalous embryos were isolated. One of the embryo snails reached the adult stage but did not lay any eggs.